Intro to decimals
Transcript of Intro to decimals
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What is a Decimal?
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What is a decimal?
A decimal is similar to a fraction – It’s not a whole number.
Rather than saying ½, we can say 0.50Instead of writing 1/10, we can say
one-tenth or 0.1.
It’s simply another form of a fraction.
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What is a decimal?
A decimal is a part of a number. We use decimals most often when we are talking about money.
$13.45How would you read this number?
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$13.45
Thirteen dollars and forty five cents.
Remember:
You do not need to use the ¢ when your money amount is greater than $1.
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What does the .45 mean?
.45 is the same thing as saying 45¢ . It means that it is only a part of a dollar.
It is not the whole dollar.
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Why do I have to understand decimals?
This is a good question. We need to understand what the value of
each number means in order to understand what we are talking about.
Here is an example: A shirt costs $12.05, but when I wrote the
number down I wrote $12.5. What’s wrong with this?
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Why is $12.5 wrong?
$12.5 really is saying $12.50, because when we read how much something costs it always has
two places after the decimal point.
If we don’t have a digit after the first number we must assume it is a zero. However, when we read $12.05, the zero is the place holder so we know it is 5¢ and not 50¢. That is a 45¢ difference. I can get a piece of gum for that amount!
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Let’s Look at Some Place Value
One Hundred Dollars
Ten Dollars
One Dollar
Ten Cents
Cents
1 3 7 8 2
Hundreds Tens Ones Tenths Hundredths
1 3 7 8 2
AND
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How do I read a decimal?
If you look at the number 12.3, you say: Twelve and three tenths.
If you look at the number 12.35, you say:Twelve and thirty-five hundredths.
If you look at a number 12.05, you say:Twelve and five hundredths.
Now you practice saying them!
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Let’s Write these Numbers in Expanded Form
$100 + $30 + $7 + 80¢ + 2¢ = $137.82
If we are using money, it would look like this:
If we are using decimals, it would look like this:
100 + 30 + 7 + .8 + .02 = 137.82
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How do I Compare and Order decimals?
7.3 and 7.03 – Which is larger?
ORGANIZE – Write the numbers vertically by lining up the decimal points.
7.37.03
EQUALIZE – Add a zero to make the numbers all have the same number of digits
7.307.03
ORDER – Start with the largest place and compare the decimals.
7.30 > 7.03
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Compare and Order – Another Example
Order from least to greatest: 12.34; 12.4; 12.43; 12.3
ORGANIZE – Write the numbers vertically by lining up the decimal points.12.3412.412.4312.3
EQUALIZE – Add a zero to make the numbers all have the same number of digits12.3412.4012.4312.30
ORDER – Start with the largest place and write the decimals in order.
12.30; 12.34; 12.40; 12.43
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When else do we use decimals?
• Weight (He weighed 85.5 lbs)
• Temperature (It was so cold today, it was only 43.7°)
• Measuring distances (example: the race was a 5 kilometers or 3.1 miles long
• Can you think of any other times?